diameterDiameter2002-02-15 17:18:052002-02-15 17:18:05Definition%\usepackage{graphicx}
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\newcommand{\mathbb}[1]{\mathbbmss{#1}}Let $A$ a subset of a pseudometric space $(X,d)$. The \emph{diameter} of $A$ is defined to be
$$\sup\{d(x,y) : x\in A, y\in A\}$$
whenever the supremum exists. If the supremum doesn't exist, diameter of $A$ is defined to be infinite.
Having finite diameter is not a topological invariant.